Have you consistently changed the brake fluid since you have owned it? Brake fluid in todays modern vehicles needs to be changed every 30k miles as preventative maintenance. I have the same thing going on right now in my vehicle. Here are the options. It could be:
A. Bad rear wheel speed sensor in the rear differential (if applicable.)
B. Bad ABS speed sensor on one of the four calipers (if applicable)
C. Bad ABS controle module (doubt it, but possible.)
D. Bad brake fluid level sensor.
Brake fluid is hydroscopic and binds with water and will eventually, if not changed, corrode the electrical components of your ABS and braking system. When this occurs, it can be boo-coo money to fix.
Here is my suggestion, read up on your vehicle on one of the many chevy forums and find other people that have experienced the same problem. Then go to your local Harbor Freight and purchase the $120 scanner that does check engine lights, ABS, transmission codes and SRS codes. Outstanding scanner for the price, considering that if you took your vehicle to a mechanic, the would charge $100 to scan the same thing. Then use the information from the scanner, coupled with your research to diagnose the problem and correct it. The good news is that ABS is not mandatory and that your vehicle will still operate while you are fixing it and/or waiting to allocate the funds necessary to fix it.
http://www.harborfreight.com/automotive-...60794-html.html
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